The present invention relates to a method for forming a capacitor, and more particularly to a method for forming a capacitor capable of preventing the generation of cell-to-cell bridges upon the formation of cylindrical metal storage nodes.
A capacitor has a structure in which a dielectric layer is interposed between a storage node and a plate node. The capacitance is proportional to the surface area of the node and the dielectric constant of the dielectric layer and inversely proportional to the distance between the nodes, i.e., the thickness of the dielectric layer. Therefore, in order to achieve high capacitance, it is necessary to use a dielectric layer having a high dielectric constant and/or enlarge the surface area of the node and/or reduce the distance between the nodes.
A concave-type silicon-insulator-silicon (SIS) capacitor which employs poly-silicon as node materials has been conventionally used. However, such a concave-type SIS capacitor has difficulties in decreasing the surface area and increasing the height of the capacitor due to reduction in the cell size, which limits the SIS capacitor's ability to secure the capacitance. Further, although research concerning dielectric layer having a larger dielectric constant has been actively conducted in a variety of ways with regard to terms of structure and method, leakage current increases the difficulty of using a dielectric layer having a larger dielectric constant.
Therefore, a capacitor has been recently developed which employs metals of higher work function as the node materials. Moreover, the capacitor structure is changed from concave to cylindrical, since the smaller size of the storage node limits the extent to which the height of the capacitor may be increased.
On the other hand, when forming the cylindrical metal-insulator-metal (MIM) capacitor using the metal node, a mold insulating layer of oxide layer must be removed after forming the cylindrical metal storage node. For these purposes, a cleaning process using a Buffered Oxide Etchant (BOE) was conventionally implemented.
Hereinafter, the conventional cleaning process which removes the mold insulating layer upon forming the cylindrical MIM capacitor will be briefly described.
First, in order to remove the mold insulating layer, the cleaning process is performed by immersing a semiconductor substrate with the metal storage node in the BOE bath containing BOE solution layer. The resulting substrate with the mold insulating layer being removed is moved into a rinse bath, where it is rinsed with deionized water in order to remove BOE chemical residues. Subsequently, the rinsed resulting substrate is moved into another rinse bath, where it is finally rinsed with the deionized water in order to remove any particles. Then, the final rinsed substrate is moved into a dryer, where it is dried. The drying process is performed using an isopropyl alcohol (IPA) vapor dryer, a Marangoni dryer, or an IPA vapor spray dryer.
In the prior art described above, however, the substrate is exposed to the atmosphere each time the substrate is moved to different bathes (i.e., chambers) for performing the cleaning process, rinse process, resulting rinse process, and drying process, and these exposures lead to certain portions of the substrate being dried out. As a result, watermarks are generated between neighboring cylindrical metal storage nodes. Such watermarks may be generated even when the water in the substrate is not completely substituted into the IPA during the drying process.
FIG. 1 shows examples of such watermarks 120 generated upon the formation of the cylindrical metal storage node. It can be noted from FIG. 1 that the watermarks 120 are generated between the neighboring cylindrical metal storage nodes 110.
However, if watermarks are generated between the cylindrical metal storage nodes, the watermarks may apply surface tension to the side walls of the neighboring cylindrical metal storage nodes such that cell-to-cell leaning is caused, thereby creating cell-to-cell bridges as shown in FIG. 2. It is impossible to repair such cell-to-cell bridges, which reduce the manufacturing yield of the semiconductor device.